Can I use a 4mm T&E for a 7.5Kw shower?

[johntheo]

9 kw is the norm around here, mostly pumped but mine is mains as I have 3.5bar constant. They are a bit on the mean side but have nice spray patterns to give ~ 3.7LPM in the winter (5/40C) & ~ 5.9LPM in high summer (18/40C).

 

[wigwamabama]

Hello telectrix,

I have regularly measured the temperature of Mains water to show people the BIG difference in Summer / Spring water temperatures compared to an average cold Winter day or night Mains water temperature - usually relating to them asking why their Combi Boiler or Electric Shower water temperature is not hot enough.

Mains water incoming pipework is supposed to be at least 750mm / 30" below the ground externally to prevent the water freezing in Winter and to prevent the water warming up in Summer / Spring.

However even at that depth below the ground the average Summer temperature measurements that I have found range from about 15 to 18 degrees centigrade.

However on cold Winter days and nights the range has been from about 3 to 5 degrees centigrade - a BIG difference regarding the incoming water temperature to Combi Boilers and Electric Showers which have a limited Heat Up / Temperature rise for the Hot water.

At my own Home on cold Winter days I have often measured the incoming Mains water temperature at only 3 degrees centigrade - Drinking water in my Fridge was 4 degrees centigrade

I have frequently seen Homes that had either inferior models of Combi Boilers or old Combi`s that were doubtless scaled up inside the Hot water Heat Exchanger where the residents have had to run Baths using the Hot tap only and then have to get straight into it before it gets too cold.

Also Homes where usually inferior models or low wattage Electric Showers could not raise the Mains water temperature to more than tepid unless the water flow volume was turned down so low that it was no more than a trickle - no Showering possible.

Chris

And what is wrong with filling a bath from the hot tap only, if you have a combi boiler? Surely it's more ridiculous to use large amounts of gas to heat the bath water, and then turn the cold tap on just to make it cold again?

 

[Davey251086]

6mm or above all day long, cable needs upgrading. Even with 6mm cable im still going out to jobs were plumbrrs have fit 9.5kw showers in with burnt up isolators causing tripping.

 

[DPG]

6mm or above all day long, cable needs upgrading. Even with 6mm cable im still going out to jobs were plumbrrs have fit 9.5kw showers in with burnt up isolators causing tripping.

Burnt out isolating switches is not down to the cable size though.

 

[Mikegh]

Burnt out isolating switches is not down to the cable size though.

No mainly down to cheap isolators, poor install, load switching etc.

The best shower isolator is one u don't switch off or crabtree or equivalent

 

[Davey251086]

Burnt out isolating switches is not down to the cable size though.

I agree a 100 per cent that the main reason a shower switch burns out is down to a loose terminal connection or cheap shower switch especially where we as sparks are cramming a 10mm cable into a 47mm pattress on the wall loosing them in the process.

However from my experience if your over-rate your cable from say a 9.5kw shower on a 6mm cable it can cause heat to dissipate anywhere on the cable. So where theres a big box on the wall full of single insulated cables with no heat to escape you see it travel all up the cable.

Some ive seen so bad the the whole cable has had to be replace. Simarily to where the cable has been bent or weakened through installation. Heat is going to affect the cable where it is most weak first so at joins or switches.

Still it takes a long time for a 9kw shower to cause the cable to burn up as its never running at full load most of the time.

 

[Mikegh]

Don't they run at full load continuous on full power ?

Or am I missing something ?

 

[James]

Don't they run at full load continuous on full power ?

Or am I missing something ?

Only for short durations, it is rare for that to be the case for hours and hours.

 

[Mikegh]

Only for short durations, it is rare for that to be the case for hours and hours.

Ah right I'm probably misinterpreting the post

The shower is on for a short period of time then ?

 

[James]

What I was getting at, is nearly all showers are only used for short durations.
not normal for one to be in use for several hours in one continuous go.

 

[Davey251086]

Don't they run at full load continuous on full power ?

Or am I missing something ?

Good question, think theres loads of factors like how hard the water is, limescale, how cold the water is, how loose the connections are to how much juice these bad boys need to perform at the right temperature.

Like a cold frosty day on an old shower with hard water surely its full load constantly.

Be one for the manufactures that one as its the appliance that determines the load required to do its job.

Id say same as james.

You could always put a clamp meter on wack it on full power and watch what happens on a cold day vs a hot day e.t.c.

But im sure we all have better things to do ?

 

[Mikegh]

What's the biggest brand in the UK then

Triton seems to be rated higher than Mira here and there was load of problems with the Mira qt apparently

I usually take away the old elite 2 and ST when fitting a shower to keep for my own place, they don't give much trouble

Load of spares I can't be doing with paying for showers for myself

 

[Davey251086]

What's the biggest brand in the UK then

Triton seems to be rated higher than Mira here and there was load of problems with the Mira qt apparently

I usually take away the old elite 2 and ST when fitting a shower to keep for my own place, they don't give much trouble

Load of spares I can't be doing with paying for showers for myself

What's the biggest brand in the UK then

Triton seems to be rated higher than Mira here and there was load of problems with the Mira qt apparently

I usually take away the old elite 2 and ST when fitting a shower to keep for my own place, they don't give much trouble

Load of spares I can't be doing with paying for showers for myself

I think mira and Triton are both very good recognised brands but for me neither.

You cant best a mixer shower the flow rate is so much better. Id all always pick thst set up anyday.

Ive got a mira digital mixer at the minute. Got the best of both worlds i feel.

 

[chris murphy]

And what is wrong with filling a bath from the hot tap only, if you have a combi boiler? Surely it's more ridiculous to use large amounts of gas to heat the bath water, and then turn the cold tap on just to make it cold again?

Hello wigwamabama,

I worded that part of my reply to telectrix badly - what I was trying to describe was that the temperature rise from the very cold incoming Mains water was so poor that the people had to get into the Bath almost the minute that the Hot water from the Combi Boiler was run into it or it would have gotten too cold to bathe in.

Chris

 

[johntheo]

Good question, think theres loads of factors like how hard the water is, limescale, how cold the water is, how loose the connections are to how much juice these bad boys need to perform at the right temperature.

Like a cold frosty day on an old shower with hard water surely its full load constantly.

Be one for the manufactures that one as its the appliance that determines the load required to do its job.

Id say same as james.

You could always put a clamp meter on wack it on full power and watch what happens on a cold day vs a hot day e.t.c.

But im sure we all have better things to do ?

There is no difference in the power consumed on a hot vs cold day, you just adjust the "temperature control" which allows more or less water to flow over the heating elements.
You can change the power setting to "eco" which switches off one element, this element is generally but not always a little smaller than the other one so you may get around 60% flow on one element.
Low voltage, because power is proportional to V squared has a marked effect as well, you have no control over the mains supply but ensuring the correct sized cable will give you a 2 to 3V drop. I had, for many years, 243V (230V supply) at the shower terminals with shower running which meant my 9kw shower outputted 10kw.

 

[Petej999]

6mm or above all day long, cable needs upgrading. Even with 6mm cable im still going out to jobs were plumbrrs have fit 9.5kw showers in with burnt up isolators causing tripping.

Don't opperate the isolator under load conditions, use the control on the shower to stop it and switch the isolator off when you leave the shower r\/ bathroom

 

[Davey251086]

Don't opperate the isolator under load conditions, use the control on the shower to stop it and switch the isolator off when you leave the shower r\/ bathroom

No one said they was but i say that to the customer everytime. Its only for emergency use

 

[Davey251086]

There is no difference in the power consumed on a hot vs cold day, you just adjust the "temperature control" which allows more or less water to flow over the heating elements.
You can change the power setting to "eco" which switches off one element, this element is generally but not always a little smaller than the other one so you may get around 60% flow on one element.
Low voltage, because power is proportional to V squared has a marked effect as well, you have no control over the mains supply but ensuring the correct sized cable will give you a 2 to 3V drop. I had, for many years, 243V (230V supply) at the shower terminals with shower running which meant my 9kw shower outputted 10kw.

Interesting, i understand how a shower works but surely the element has to work harder to heat colder water same as a kettle as thats all a shower is just alot bigger version. If you have really cold water your kettle takes longer to boil.

The question to answer further above was does an electric shower run on full load constantly??

I dont believe it does because of the factors listed above.

What do you think??

 

[telectrix]

No one said they was but i say that to the customer everytime. Its only for emergency use

what use is that? you fallover in the shower, how you going to reach that pull cord 6 feet away and 4ft/above .?

 

[Mikegh]

Interesting, i understand how a shower works but surely the element has to work harder to heat colder water same as a kettle as thats all a shower is just alot bigger version. If you have really cold water your kettle takes longer to boil.

The question to answer further above was does an electric shower run on full load constantly??

I dont believe it does because of the factors listed above.

What do you think??

Kettle has to raise water to boiling point so colder water takes longer

Shower is just instantaneous heater ,turns on and heats what passes through it